The Story Of Kraftwerk, the BBC radio documentary from 2008, is available to stream in full (in four parts) below! Bonus: the documentary was narrated by Alex Kapranos from Franz Ferdinand! For those who prefer video documentaries, another Kraftwerk film from 2001 is also posted below along with a Kraftwerk television special which aired on German television in 1981.
Kraftwerk documentary, 2001
German television special, 1981